Microelectromechanical systems (MEMS) technology has been under steady development for some time, and as a result various MEMS devices (including gyroscopes) have been implemented within several applications. MEMS gyroscopes generally belong to a vibratory mass class of gyroscopes. The vibratory MEMS gyroscopes are the devices used to measure rate of rotation. In general, there are two sub-classes of vibratory mass gyroscopes: (1) in-plane rotation sensors (also referred to as “X/Y rate sensors”), and (2) perpendicular-to-the-plane rate sensors (also referred to as “Z-axis (angular) rate sensors”). Although X/Y rate sensors and Z-axis rate sensors operate in accordance with the same principals, there are fundamental design differences between the two classes of gyroscopes—e.g., structural designs associated with one class cannot be easily extended to the other class.
A fundamental challenge with design of MEMS Z-axis rate sensors is to develop dual mass vibrating masses that vibrate 180 degrees out of phase, and develop ability to capacitively sense a Coriolis force exerted on the vibrating masses through sensing a motion of a rotating frame around the Z-axis. When sensing the Coriolis force it is desirable to minimize any quadrature effects—e.g., the coupling of the drive vibration to the sense frame—in order to have a good signal to noise ratio. Another challenge of designing MEMS Z-axis rate sensors is achieving a design that permits such sensors to be fabricated in high volumes and with low costs to address consumer market needs and address high volume applications (e.g., gaming applications, GPS assist applications, and mobile handset applications, and so on). Yet other desired design objectives are to provide for a reduced (e.g., minimal to none) sensitivity to linear vibrations, and also a robust design that can with stand high level of shock, e.g., due to a product being dropped.
Today, the costs associated with conventional Z-axis rate sensors are generally prohibitive for any use in the consumer market, and conventional Z-axis rate sensors also are not the most efficient in terms of size and power consumption. A main factor associated with the cost of a MEMS Z-axis rate sensor is the packaging associated with the MEMS Z-axis rate sensor. Conventional MEMS gyroscope solutions typically rely on hermetic ceramic packages having a controlled ambient in vacuum to deliver a required performance. It is virtually impossible to deliver to the consumer market a MEMS Z-axis rate sensor that meets cost/performance requirements without addressing packaging cost issues.